A sensor system detects a presence or concentration of an analyte in a medium. The sensor system contains a sensor having a sensor head with a chamber. The sensor head has a permeable area through which the analyte can pass into the chamber when the sensor head contacts the medium. A cross-linked hydrogel fills the chamber, the hydrogel is configured to undergo a change in volume when contacting the analyte passed into the chamber which leads to a change in pressure in the chamber. A pressure sensor is configured to measure the pressure in the chamber for detecting the presence or concentration of the analyte.